Sunday, January 23, 2011

Easy data caching in Rails 3

Three common forms of caching

There are 3 types of caching that are very commonly talked about in the rails community; page caching, action caching, and fragment caching. All of these are well documented and are great ways to cache varying amounts of content for your pages.

Is that all the caching I need?

Caching at the view level is great but it isn't necessarily the best fit for every situation. In some cases it may be easier to cache data at a lower level. Perhaps you want to cache the results of an external data request for a given period of time. None of the view caching methods would be a really great fit.

Lower level data caching

Rails 3 actually has a great method for caching data at a lower level than the view. It even uses the same caching store as action and fragment caching. ActiveSupport::Cache::Store allows you to store any serializable Ruby object. Rails even provides an already initialized cache store via Rails.cache.

Example usage and code

I used this on www.checkthesock.com to cache METAR queries. I was using current_metar a gem I built that pulls metar data from ADDS. I made a model called CachedMetar to return cached results to the rest of my application.

Code walk through

This model basically returns the result of the block argument to Rails.cache.fetch the first time it is called. Any time it is called within the next 5 minutes it returns the value that was cached the first time. Everywhere I had previously been calling CurrentMetar::Metar.get_metar("ICAO code") I switched to call CachedMetar.metar("ICAO code") and that was all it took.

Testing

Testing is actually surprisingly easy. I used shoulda and mocha and here is what I ended up with.

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